As a conventional driving force transmission apparatus, there is a driving force transmission apparatus which is installed in, for example, a four-wheel drive vehicle and in which a pair of rotational members are connected together by a clutch so as to transmit torque (refer to Patent Literature 1, for example).
This driving force transmission apparatus includes a first rotational member which rotates together with an input shaft, a second rotational member which can rotate on an axis of the first rotational member, a friction-type first clutch which connects the second rotational member and the first rotational member together so that torque can be transmitted therebetween, an electromagnetic clutch which is aligned in parallel to the first clutch along the axes of the first rotational member and the second rotational member, a friction-type second clutch which receives an electromagnetic force of the electromagnetic clutch to operate, and a cam mechanism which transforms a rotational force from the first rotational member to a pressing force towards the first clutch side by the clutching operation of the second clutch.
The first rotational member includes a bottomed cylindrical front housing which is opened at one end and an annular rear housing which is installed in an opening portion of the front housing and is connected to the input shaft. Then, the first rotational member receives a driving force of a drive source such as an engine of the vehicle from the input shaft to rotate.
The second rotational member is disposed so as to rotate relatively to the first rotational member on the rotational axis thereof and is connected to an output shaft.
The first clutch has an inner clutch plate and an outer clutch plate and is disposed between the first rotational member and the second rotational member. Additionally, the first clutch functions as a main clutch and connects the first rotational member and the second rotational member together so that torque can be transmitted therebetween as a result of the inner clutch plate and the outer clutch plate being brought into frictional engagement with each other.
The electromagnetic clutch is disposed on the axes of the first rotational member and the second rotational member. Then, the electromagnetic clutch generates an electromagnetic force to operate the second clutch.
The second clutch has an inner clutch plate and an outer clutch plate and is disposed on an electromagnetic clutch side of the main clutch. Then, the second clutch functions as a pilot clutch which receives the electromagnetic force of the electromagnetic clutch to operate and imparts the rotational force from the first rotational member to the cam mechanism.
The cam mechanism has a pressing portion which imparts a pressing force to the first clutch through a cam action resulting from the rotational force from the first rotational member and is disposed between the first rotational member and the second rotational member.
Based on the configuration described above, when the driving force from the engine side is inputted into the first rotational member via the input shaft, the first rotational member rotates about the axis thereof. Here, when the electromagnetic clutch is energized, the second clutch operates based on the electromagnetic force of the electromagnetic clutch.
Next, when the cam mechanism receives the rotational force from the first rotational member when the second clutch is in operation, this rotational force is transformed into the pressing force by the cam mechanism, and this pressing force is imparted to the first clutch.
Then, the inner clutch plate and the outer clutch plate of the first clutch are closed to each other and brought into frictional engagement with each other, and the first rotational member and the second rotational member are connected together so that torque can be transmitted therebetween by the frictional engagement. This enables the driving force on the engine side to be transmitted from the input shaft to the output shaft via the driving force transmission apparatus.